1) Field of the Invention
The present invention relates to an electric discharge machining apparatus having a function of simulating, before performing the electric discharge machining, the machining state of a workpiece that is worked by a discharge electrode, and an electric discharge machining simulator having the function of simulating.
2) Description of the Related Art
A rough machining condition of the conventional die-sinking electric discharge is determined substantially based on a machining area, in view of electrode wear and critical current density. For example, a machining condition with respect to a narrow machining area requires low energy, and a machining condition with respect to a wide machining area requires high energy. It is preferable that the machining condition is changed as the machining area changes by machining. The machining time is basically calculated by the following expression:Machining time=machining volume/machining volume per unit time. 
From this expression, it becomes possible to estimate machining time accurately if accurate machining volume can be obtained. However, the work piece machined by the die-sinking electric discharge actually has a complicated shape. Therefore, most of the operations for determining the machining condition and estimating the machining time have to depend on the intuition and experience of an operator, except for machining for simple shapes such as a cylinder or a quadratic prism obtained by machining a raw material.
On the other hand, a method is known in which such a dependency on the intuition and experience of the operator is small and the machining condition for more accurate machining is determined. The method includes predicting a sectional area to be machined while confirming the discharge state during machining, and adjusting the machining condition based on the predicted sectional area.
Furthermore, another method is proposed in which the machining condition is determined with a specific sectional area as the machining area. The specific sectional area is an area sliced in an electrode shape or a final metal mold shape with a suitable depth. A conventional electric discharge machining apparatus that determines the machining condition by such a method is explained below. FIG. 16 is a block diagram illustrating one example of a basic configuration of the conventional electric discharge machining apparatus. FIG. 17 is a block diagram illustrating the configuration of the machining condition determining apparatus equipped in the conventional electric discharge machining apparatus shown in FIG. 16. In FIG. 16, the electric discharge machining apparatus 100 includes: a machining tank 5 in which a workpiece 10 is arranged in a machining fluid 11; a machining unit 2 having a tool electrode arranged opposite to the workpiece 10; a power supply 3 that supplies a voltage between the tool electrode and the workpiece 10; a machining condition determining apparatus 7 that determines the machining condition of the workpiece 10; and a numerical control unit 4 that controls a motor (not shown) fitted to the machining unit 2 and the machining tank 5, based on the determined machining condition.
In FIG. 17, the machining condition determining apparatus 7 includes: an input section 71 that receives requirement specifications from a user; an electrode sectional area calculator 72 that calculates the sectional area of the tool electrode with an optional interval; an electrode sectional area storage 73 that stores the sectional area data of the calculated by the electrode sectional area calculator 72; a basic machining conditions storage 75 that stores basic machining conditions; a machining condition search section 74 that searches a machining condition suitable for the sectional area of the electrode, from machining conditions stored in the basic machining conditions storage 75; and an output section 76 that outputs the searched machining condition.
FIG. 18 illustrates a data structure stored in the electrode sectional area memory 73. As shown in this figure, the electrode sectional area memory 73 stores data rows in which the machining depth and the sectional area of the electrode are stored in pairs. In FIG. 18, “machining depth” represents a distance from the bottom face of the electrode in the height direction, and “sectional area to be machined” represents a sectional area to be machined by the electrode at the machining depth.
The operation of the conventional electric discharge machining apparatus 100 having such a configuration will be explained in detail below with reference to the flowchart shown in FIG. 19. First, a user of the electric discharge machining apparatus 100 inputs requirement specifications of an electrode shape a1 and machining depth a3 by the input section 71, according to specifications required for the workpiece 10 (step S101).
When receiving the requirement specifications from the input section 71, the electrode sectional area calculator 72 sets a slice depth s at −0.25 mm, where the slice depth s is the slice depth from the bottom face of the electrode shape a1 (step S102). The electrode sectional area calculator 72 calculates the sectional area of the electrode at the position of this slice depth s, and stores the sectional area of the electrode in the electrode sectional area storage 73 (step S103). Thereafter, the electrode sectional area calculator 72 sets the slice depth s at s −0.25 mm (that is, −0.50 mm) (step S104), and judges whether this slice depth s is not more than the machining depth a3 set at step S101 (step S105).
The electrode sectional area calculator 72 repetitively executes the process of from step S103 to step S104, until the slice depth s becomes not more than the machining depth a3. In other words, the electrode sectional area calculator 72 stores the sectional area data of the electrode for every 0.25 mm from the bottom face of the electrode shape a1 in the electrode sectional area storage 73, until the slice depth s becomes the machining depth a3.
Thereafter, when the slice depth s is not more than the machining depth a3 (step S105, Yes), the machining condition search section 74 searches a starting machining condition and a finishing machining condition at each depth from the sectional area data of the electrode in the electrode sectional area memory 73 (steps S106 and S107), and outputs the searched machining conditions to the output section 76 (step S108).
The numerical control unit 4 executes machining of the workpiece 10, by controlling the power supply 3 and the motor (not shown) fitted to the machining unit 2 and the machining tank 5.
In the actual electric discharge machining, however, as shown in FIG. 20A, a workpiece 10a having a prepared hole formed in the previous step, such as cuttings is to be machined, in some cases. As shown in FIG. 20B, in some cases, the workpiece 10 is machined only by a part of the electrode. In these cases, since the sectional area of the electrode shape or the final metal mold shape does not coincide with the machining area, an adequate machining condition is not selected. Further, since the conventional electric discharge machining apparatus 100 does not have a unit that confirms the workpiece before machining, there is a problem in that, for example, when the size of the electrode is not appropriate, or the machining depth is erroneously set, an existence of the error cannot be found until machining is finished.